Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $15.29   13.254%   $17.3165   $17.32   $17.30   $17.30  
  Purchase #2 $162.95   3.274%   $168.285   $168.29   $168.30   $168.30  
  Purchase #3 $37.57   13.153%   $42.5116   $42.51   $42.50   $42.50  
  Purchase #4 $208.89   7.402%   $224.352   $224.35   $224.35   $224.40  
  Purchase #5 $163.53   8.574%   $177.5511   $177.55   $177.55   $177.60  
  Purchase #6 $176.60   6.748%   $188.517   $188.52   $188.50   $188.50  
  Purchase #7 $231.27   7.683%   $249.0385   $249.04   $249.05   $249.00  
  7 purchase totals = $996.10       $1,067.5717   $1,067.58   $1,067.55   $1,067.60